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Similar medicines derived from the guaiac tree were in use as a generic remedy by American indigenous peoples when explorers reached North America in the 16th century. The Spanish encountered guaiacum wood "when they conquered Santo Domingo; it was soon brought back to Europe, where it acquired an immense reputation in the sixteenth century as a cure for syphilis and certain other diseases..."[3]

The 1955 edition of the Textbook of Pharmacognosy states: "Guaiacum has a local stimulant action which is sometimes useful in sore throat. The resin is used in chronic gout and rheumatism, whilst the wood is an ingredient in the compound concentrated solution of sarsaparilla, which was formerly much used as an alternative in syphilis."[3]

Guaifenesin was first approved by the Food and Drug Administration (FDA) in 1952. Although previously deemed "Generally Regarded as Safe" in its original approval, the drug received a New Drug Application for the extended-release version, which won approval on July 12, 2002. Because of this, the FDA then issued letters to other manufacturers of timed-release guaifenesin to stop marketing their unapproved versions, leaving Adams Respiratory Therapeutics in control of the market. Adams was subsequently acquired by Reckitt Benckiser, based on the strength of the marketing generated by Adams' Mucinex brand.[4][5]

The principal use of guaifenesin is in the treatment of coughing. A Cochrane Collaboration meta-analysis of over-the-counter medicines for acute cough in children and adults concluded that there was not enough high-quality clinical data to prove or disprove the effectiveness of any examined drug including guaifenesin.[6] Guaifenesin is sometimes combined with dextromethorphan, an antitussive, such as in Mucinex DM or Robitussin DM.[7]

The guaifenesin protocol uses guaifenesin as an unapproved fibromyalgia treatment, despite the fact that a one-year double-blind study indicates that the treatment performs no better than placebo.[8][9] Guaifenesin has not been approved by the FDA for the treatment of fibromyalgia.

Based on a small, non-blinded study,[10] guaifenesin has been promoted to facilitate conception, by thinning and increasing cervical mucus, during the few days before ovulation.[11]

Guaifenesin is thought to act as an expectorant by increasing the volume and reducing the viscosity of secretions in the trachea and bronchi. It has been said to aid in the flow of respiratory tract secretions, allowing ciliary movement to carry the loosened secretions upward toward the pharynx.[12] Thus, it may increase the efficiency of the cough reflex and facilitate removal of the secretions.

Side-effects of guaifenesin include nausea, vomiting, formation of kidney stones,[14] diarrhea, and constipation.[15] Nausea and vomiting can be reduced by taking guaifenesin with meals.[2] The risk of forming kidney stones during prolonged use can be reduced by maintaining good hydration and increasing the pH of urine. Rarely, severe allergic reactions may occur, including a rash or swelling of the lips or face, which may require urgent medical assistance. Mild dry mouth or chapped lips may also occur when taking this medication. Drinking a glass of water is recommended each time one takes guaifenesin.[16]

Guaifenesin increases the analgesic effect of paracetamol (acetaminophen) and aspirin, increases the sedative effects of alcohol, tranquilisers, sleep-pills and total anesthetics. Guaifenesin increases the effects of medication that decrease muscle tone.[citation needed]

Guaifenesin's neurological properties first became known in the late 1940s. Guaifenesin is a centrally acting muscle relaxant used routinely in large-animal veterinary surgery. Guaifenesin is used in combination with, for example, propofol, since guaifenesin does not produce analgesia nor does it produce unconsciousness.[17][18]